The Cuban authorities have launched an inquiry into how the official newspaper of the Communist party ran a front page photograph of Fidel Castro which appeared to have been doctored to make him look like Adolf Hitler.

When the edition of Granma hit the streets this month party officials began to retrieve as many copies as they could, an operation which appears to have deterred foreign journalists based on the island from reporting the story.

The picture appeared above a story which reported President Fidel Castro's meeting with North American students. Close examination of the photograph shows that the image of the Cuban leader has been subtly altered to make him look like the Nazi leader.

Underneath banners proclaiming Cuba's opposition to war and terrorism, President Castro is seen in full military uniform, but the world's most famous beard has been replaced by history's most striking moustache, while his grey hair now has the faint hint of a black comb-over.

Although details of what happened remain unclear, what is known is that someone or some group at the newspaper appears to have risked all in the name of political satire.

Yesterday a spokesman for the newspaper confirmed that an investigation was under way, but that the photographer who took the picture was not responsible.

Now the talk of Havana is not just of what the image was supposed to mean, but of what has happened to those under suspicion. Rumours have spread, not least because the local offices of the Communist party went to work as soon as the change was noticed, ensuring that fewer copies than normal made it on to the streets.

Many people did not receive their daily delivery, while those sent to offices were subsequently recalled.

Some say that those seated in the background of the photograph, which was published on December 4, have had their glasses darkened, to make them look like mafiosi, or that they have had white lines superimposed on their lips, suggesting that they dare not speak out against President Castro's wishes.

Others argue that the whole thing is nothing more than a trick of the light. But the Cuban authorities are treating the matter far more seriously than that.

There is no official word on what has happened to the suspected culprits, but rumours of arrests and a large-scale investigation have hit the Havana grapevine.

Yesterday the newspaper tried to play down the significance of the investigation. A spokesman dismissed rumours about the number of those arrested as "lies", saying that there was a single suspect.

The government has as yet made no official statement, and no story has appeared in the foreign press, leading many Cubans to question the purpose of foreign journalists based on the island.

This latest dissent highlights what some see as a changing mood in Havana.

In October dissident members of the Proyecto Varela, led by Oswaldo Payá, delivered a petition to parliament in Havana calling for a referendum on human and democratic rights. This was the second petition to be presented in the past two years and carried the signatures of more than 14,000 Cubans.

The petition has been refused by the Cuban authorities. How many others privately agree with Mr Payá is impossible to gauge, but this most recent example of dissent against President Castro suggests a new mood.

In April the president provoked international criticism in his most brutal crackdown on dissent since the early years of the revolution in the 1950s.

More than 80 journalists, economists and librarians were arrested and hastily tried, with some of the leading voices of dissent among those sentenced to prison for up to 30 years.

The brief trials saw former colleagues and aides used as witnesses, accusing them of "activities against the integrity and sovereignty of the state" and of having worked as infiltrators on behalf of the US.

Young Cubans, particularly in Havana, have failed to immerse themselves in the revolutionary ideals to the same extent as those born before 1959 and President Castro's triumph over the former rightwing dictator Fulgencio Batista.

With the collapse in 1989 of the Soviet Union - Cuba's main international source of financial and political support - the island has been forced to turn to tourism.

Although this has brought in much needed dollars, and helped to fund education and healthcare, it has also been the source of discontent.

Wealthy foreigners parade along the streets of the capital, carrying digital cameras, mobile phones and wearing the kind of expensive sportswear of which the average Habañero can only dream. It is no surprise then that young Cubans look on enviously, while turning their backs on the Communist ideology that preaches against western consumerism. But, with the regime as vigorous as ever in clamping down on opposition, they may yet have to wait for change.